Process and apparatus for cementing oil wells



y 1939- I P. s. PUSTMUELLER 2,160,228

PROCESS AND APPARATUS FOR CEMENTING OIL WELLS Original Filed April 11,1938 2 Sheets-Sheet l zil I V I W it Fig. l

1 Fig.3

lnvenior: Poul S. Pusi'mueller Fig. 2 by his A++ome m 2 Sheets-Sheet 2Fig. 7

P. s. PUSTMUELLER Original Filed April 11, 1938 PROCESS AND APPARATUSFOR CEMENTING OIL WELLS May 30, 1939.

\nvenror: Paul S. Dusrmueller 5g his Afforneg: MW

Patented Ma 30, 1939 I v 2,160,228

UNITED STATES PATENT OFFICE PROCESS AND APPARATUS FOR CEMENT- ING OILWELLS Paul s. Pustmueller, Bakersfield, Calif., assignor to ShellDevelopment Company, San Francisco; Oalit; a corporation of Delaware 1application April 11, 1938, Serial No.

201,346. Divided and this application December 19, 1938, Serial No.246,617

' Claims- (Cl. 166-1) The present invention pertains to the art ofmixture through suitable passagesinthe shoe into cementing oil and gaswells, and is more particuthe annular space 2 between the casing and thelarly related to a process whereby the shoe or walls of the borehole, acertain amount of'cement lower end of a casing string may be cemented at4 remaining also in the lowest section of the casan intermediate levelof the well, that is, at ing. After the cement has 'set, a drill bit isa point relatively distant from the bottom of the lowered within thecasing, and a hole 6 is drilled hole, and a bridging cement plug,necessary for through the hardened cement remaining in the testing theefliciency of water shut-off obtained by easing, through the casing shoeand through the cementing the casing, may be placed below the formationbelow the plug, usually to a distance i casing shoe in a singleoperation without moving not exceeding five feet of said formation. A 10the casing. formation tester 3 such, for example, as the The presentapplicationis a division of my co- I-Ialliburton or the Johnstonformation tester, is pending application Serial No. 201,346,1iled Aprilthen anchored in the hole drilled through the 11, 1938. cement plug, andthe efllciency of the water shut- 5 The present invention will beunderstood from off is determined by observing the fluid passing thefollowing description, taken with reference through said tester, anadmixture to said iiuid of to the attached drawings, wherein: a brinedue to leakage through or around the Fig. 1 diagrammatically illustratesa convencement plug from the water layer W indicating tional applicationof the water shut-oi! test to a in such cases an imperfect cementing ofthe cas- D casing string cemented near the bottom of the ing. a0

borehole. In some cases, however, it may be found desir- Fig. 2diagrammatically illustrates a convenable to cement the casing shoe at apoint contionalapplication of the water shut-ofl test to a siderablyabove the bottom of the hole. This is casing string cemented in anintermediate zone done, for example, when the whole, or at least a I ofthe well. portion of a producing sand has been penetrated, 5

Fig. 3 diagrammatically illustrates the applicaor the well has beendrilled for coring or logging tion of the water shut-off test to acasing string purp se to its total pt before the most adcemented in anintermediate zone of the well 3.0- vantageous point f r cementing theshoe of the cording to the method of the present invention. casing isdetermined.

*0 Fig. 4 is an elevation view in cross section of a In such cases, asshown in Fig. 2, if .the casing preferred embodiment of the apparatus ofthe shoe I5 is lowered to the desired level A, and cepresent invention.ment is pumped down and out therethrough, the

Fig. 5 is a plan view of the open seat valve effect of the drillingfluid standing in the boreshown in Fig. 4. I r hole and havingapproximately the same coni5 Figs. 6 and? are elevation views in crosssection sistency andspecitlc gravity as the cement will of otherpreferred embodiments of the tailpiece not permit the cement to settlefor more than 1' is shown in Fig. 4. v or 2 feet below the shoe, thecement being there- Present 011 field practice requires that wells foreforced upwards around the casing. when,

be properly cased and cemented off in order however, ahole is drilledthrough the casing shoe to to prevent the dissipation of oil depositsinto in orderto apply a water shut-off test as before, 4.0non-productive strata or to protect said deposits it is obvious thatsuch test will not be conclusive against contamination by aqueousliquids from as to the efficiency of the cement plug placed in adjacentformations. Some State laws prescribe the annular space behind thecasing, since it it that the effectiveness of cementing operations innotknown whether any brine flowing through the shutting off fluid flowbehind the casing be in each formation tester 3 is {due to leakage fromthe case tested according to definite regulations. upper water layer Wthrough or around the Whenever it is desired to cement a casing stringcement plug surrounding the casing, or to a flow extending substantiallyto the bottom of the boreof brine from a lower water layer L; In suchhole, the cementing operation and the water shutcases, therefore, it iscustomary to place, as a preoff test do not present especialdifficulties. In liminary operation, a bridging plug 1 at some 5 Suchcases as Shown in 1 h asin shoe point below the cementing level 8 toseal 01! the 5 is lowered at the end of a casing string i subportion ofthe'well extending below the casing stantially to the bottom'ofthe'hole, a desired shoe 5. quantity of a cementing mixture is loweredinto The placement of the bridging plug 1 is usually the casing, andpressure is applied to force said carried out by one of the followingmethods:

1. A desired quantity of cement may be spotted to the level i. by meansof bailers and left to set there, whereafter the casing shoe is loweredto the levelA and cemented there in the usual manner.

2. A string of tubing is lowered to the level I, and a desired quantityof cement is pumped down therethrough, whereafter the tubing string iswithdrawn, the bridging plug I left to set, and the casing cemented atlevel A as before.

3. The casing string I is first lowered to level I, a desired quantityof cement is pumped therethrough to form the bridging plug 1, whereafterthe casing string is raised to level A, the bridging plug at l is leftto set, and the casing is finally cemented at level 6, the watershut-off test being then carried out as before.

In using method 1 or 2, great difiiculties are often experienced inplacing an effective bridging plug due to admixture of the cement slurrywith the drilling fluid in the borehole. Bridging operations mustsometimes be repeated three or four times before a satisfactory bridgingplug is placed,

. which entails a considerable loss of time and increases the cost ofcementing operations. Moreover, even when the bridging operation hasbeen successfully carried out, a loss of time is experienced since thebridging plug must be allowed to set before the main cementingoperation, that is, the cementing of the casing shoe, may be performed.

The use of method 3 involves the additional danger of freezing thecasing string at the level 1, that is, below the desired level A, due toa premature setting of the cement, and should not be attempted at anydepth greater than 4000 feet.

All three of these methods have the additional drawback of badlydamaging thedrilling fluid system by contamination with cementing slurryduring the bridging operation. Since it is especially important to havethe drilling fluid in good condition at the time, when the casing stringis being set to prevent freezing due to the effect of settling cuttingsor sloughing formations, a cementing method which eliminates thenecessity of a separate bridging operation becomes of considerablevalue.

Furthermore, the circulation of a cement-contaminated drilling fluid incontact with the face of oil-bearing sands often causes a partialplugging of the latter and results in wells of reduced productivity.

It is therefore the object of the present in vention to provide a methodand an apparatus for cementing a string of casing in an intermediatezone of the well and for placing a bridging cement plug below the casingshoe at the time and as a part of the regular casing cementingoperation, whereby the time necessary for such operation is considerablyreduced, and the danger of contaminating the drilling fluid during thebridging operation is eliminated.

Referring to Fig. 4, the apparatus of the present invention comprises astring of casing I, supporting a casing shoe 5, made of or comprising adrillable material such as cast iron, aluminum, bronze, cement, or anycombination of these or similar materials. The casing shoe comprises avalve, such as a ball valve 15, or a non-return valve of any otherdesired type. The ball valve I5 is held within a housing l8, having anaxial passage l2 forming an upper seat adapted to close the valveagainst any upward fluid flow, and with a downward axial passage I!provided with an open seat l6, shown in detail in Fig. 5,

which permits a downward flow of fluid through the valve. The housing i3is also provided with ports and passages M, leading through the casingshoe upwards and at an angle designed to give the fluid passingtherethrough a whirling motion on issuing out of the shoe. Thecross-sectional area of the passages I4 is adjusted in such manner withregard to the cross-sectional area of the main downward passage N, thatthe liquid passing through the valve is automatically proportioned intostreams having any desired capacity ratio, for example, 40 percentthereof passing through the whirler ports l4, and 60 percent through themain downward passage H.

A drillable swage I8 is attached to the lower portion of the shoe 5, andserves to support the tail piece or tubing section l9, which haspreferably an outside diameter smaller than the inside diameter of thecasing string, and is made of an easily drillable material such asaluminum, Bakelite, hard rubber, brass, cast iron, etc. The tail piece19 is usually from 10-to 20 feet long, being closed at the bottom by ascrew plug 2!, made of the same material, and provided in its lowerportion with perforations 20 to permit a fluid flow therethrough.

As shown in Fig. 6, a drillable float shoe 5A, provided with a valvesimilar in construction to that of the casing shoe 5, may be used ifdesired instead of the screw plug 2| at the lower end of the tail piece19, or said lower end may be left open, as shown in Fig. '7. It maylikewise be desirable to provide the tail piece I9 with inside oroutside rifling, or both, as shown at 22 and 23 in Fig. '7. This riflingmay be grooved on or attached to the tail piece in a manner well knownto the art, and serves to give the cement slurry descending through thetail piece or ascending around it a whirling motion.

In placing a bridging plug and cementing a casing string in anintermediate well zone, that is, at a point considerably above thebottom of the borehole, the following procedure may be followedaccording to the present invention.

Referring to Fig. 3, the casing shoe 5, provided with the tail piece I9,is lowered into the borehole at the end of a casing string and placed atthe exact level A where it is to be cemented, the tail piece l9extending to approximately from 10 to 20 feet below said level. Adesired amount of cement, such, for example, as three to five hundredsacks, or more, is then made into a slurry of any desired water content,and is pumped down the casing, followed by a solid wooden or rubber plugto which fluid pressure is applied from the top. The cement slurry isthereby forced out of the casing, a certain proportion thereofissuingthrough the whirler ports l4 into the space around the casingshoe, and another portion issuing through the perforations 2! in thelower portion of the tail piece I9 into the space around said tailpiece. The borehole being filled with a drilling fluidgwhose consistencyand specific gravity do not greatly differ from that of the cementslurry, the latter has no tendency to settle down to a greater distancethan 1 or 2 feet below the plug 2|, and is forced upwards to a pointconsiderably higher than the casing shoe 5, completely filling theannular space between the casing, casing shoe and tail piece, and thewalls of the borehole. When the wooden or rubber plug following thecement charge within the casing string strikes the casing shoe 5, or aspecial stop for said plug provided .within the casing string at somedistance, such as one casing stand damage #1 above the casing shoe, thefluid flow is stopped, and a rise of pressure indicates to the operatorthat the whole of the cement slurry has been forced into the borehole,excepting a small portion within the casing and tail piece below saidwooden plug. The cement slurry is then allowed to set, a considerablesaving of time being effected due to the fact that the bridging plug,that is, the cement within and around the tail piece Hi, can be allowedto set at the same time with the cement used for the main cementingoperation, that is, with the cement in the annular space around thecasing string I. In view of the fact that the bridging plug is placedwithin and around the tail piece l9, which serves as a metallic memberreinforcing the cement, the cement slurry has no appreciable tendency tomix and be diluted or absorbed by the drilling fluid within the boreholeand the formation of the bridging plug is thereby positively insured.

After the cement slurry has set, a drill bit is lowered within thecasing string, and the hardened cement within the lowest casing joint,the friable casing shoe, as well as the upper portion of the tail piecel9, together with the cement in which it is embedded, is drilled out toa distance not exceeding about 5 feet below the casing shoe, that is, toa distance equal to approximately from one-fifth to one-half of the tailpiece l9, as shown at 6 in Fig. 3. A formation tester 3 is then anchoredwithin the hole thus drilled, and a water shut-off test is run in theusual manner 7 It will be noted that, although the space 6 is notactually in contact with the formation through which the well has beendrilled, the annularbody of cement 9 separating said space from thewalls of the borehole has a relatively small thickness, such as about 2inches, and is, moreover, considerably cracked and damaged during thedrilling of the space 6, being therefore quite pervious to fluid flow.Suitable and well known means may furthermore be used to break and/orremove said annular body of cement. If, therefore, the cement plugaround the casing string, or the bridging plug around the tail piece l9,have been imperfectly placed, and leakage through or around said plugtakes place from any upper water layer, the leaking fluid will easilypenetrate into space 6, and can be detected by means of the formationtester.

I claim as my invention:

1, In a process for cementing a well casing, the steps of attachingthereto a shoe supporting a drillable tubing section of substantiallength, said shoe having transverse passages communicating with theoutside of the casing and a downward passage coaxial with said tubingsection, lowering said shoe to the desired level within the borehole,lowering a cement slurry into said casing and tubing, applying downwardpressure thereto within the casing, forcing said slurry out of thecasing shoe passages and out of the lower end of the tubing, and causingsaid slurry to fill the annular space between said casing and tubing andthe walls of the borehole to a point above the casing shoe.

2. In a process for cementing a casing string at an intermediate levelof a borehole filled with a drilling fluid, the steps of attaching tosaid casing a drillable shoe supporting a drillable tubing section of asmaller diameter than said casing, said shoe having transverse fluidpassages communicating with the outside of the casing,

ing section, lowering said shoe to the desired level within theborehole, lowering a cement slurry into said casing and tubing, applyingdownward pressure thereto within the casing, forcing a portion of saidslurry out of the casing through the transverse passages of the shoe,forcing another portion of said slurry out of the lower end of thetubing, causing said slurry to fill the annular space between saidtubing and casing and the walls of the borehole to a point above thecasing shoe, discontinuing the pressure when substantially all theslurry has been driven out of the casing, allowing the tubing to remainfilled with the, slurry, allowing the slurry within the borehole to set,lowering a drill bit within the casing, drilling out the casing shoe,and not more than five feet of the\ upper portion of the tubing, andtesting the space thus drilled out for the leakage of fluids l throughthe cement plugs formed above the casing shoe.

3. In an apparatus for simultaneously cementing a casing in a boreholefilled with a drilling fluid and placing a bridging plug below the shoeof said casing, a casing strip, a shoe attached to the end of saidcasing,transversepassagesthrough said shoe in communication with theoutside of the casing, an axial passage through said shoe, and adrillable tubing section supported by the shoe and coaxial with saidlast passage, said tubing section having an outside diameter smallerthan the inside diameter of the casing.

4. In the apparatus of claim 3, a spiral rifling on the outside wall ofthe tubing section.

5. In the apparatus of claim 3, a spiral rifling on the inside wall ofthe tubing section.

6. In the apparatus of claim 3, a spiral rifling on the inside andoutside walls of the tubing section.

7. In an apparatus for simultaneously cementing a casing in a boreholefilled with a drilling fluid and placing a bridging plug below the shoeof said casing, a casing string, a drillable shoe attached to the end ofsaid casing, transverse passages through said shoe in communication withthe outside of the casing, an axial passage through said shoe, adrillable tubing section supported by the shoe and coaxial with saidlast passage, said tubing section having an outside diameter smallerthan the inside diameter of the casing, a plug closing the lower end ofsaid tubing section, and a plurality of perforations in the lowerportion of said tubing section above said plug.

8. In an apparatus for simultaneously cementing a casing in a boreholefilled with a drilling fluid and placing a bridging plug below the shoeof said casing, a casing string, a drillable shoe attached to saidcasing, a vertical passage through said shoe, a non-return valveallowing a downward fluid flow within said passage, means compr sing aplurality of fluid passages in communication between said valve and theoutside of the shoe for causing a predetermined proportion of the fluidpassing downwardly through the valve to issue through said passagestransversely of the shoe, and a drillable tubing section supported bythe shoe and coaxial with the vertical passage through the shoe, saidtubing section having an outside diameter smaller than the insidediameter of the casing.

9. In the apparatus of claim 8, a drillable shoe attached to the end ofsaid tubing section, a vertical passage through said shoe, a non-returnvalve allowing a downward flow through said passage, and a plurality oftransverse fluid passages in communication between said valve and theoutside of said shoe.

10. In an apparatus for simultaneously cementing a well casing in aborehole filled with a drilling fluid and placing a bridging plug belowthe shoe of said casing, a casing, a shoe attached to the end of saidcasing, transverse passages through said shoe in communication with theoutside of the casing, an axial passage through said shoe, and adrillable tubing section supported by the shoe and coaxial with saidlast passage, the lower outlet of said tubing section being at a 5substantial distance below the casing.

PAUL S. PUSTMUELLER.

